http://www.freecodecamp.com/mattnwa 's solution for Bonfire: Mutations

bonfire-mutations.js

// Bonfire: Mutations
// Author: @mattnwa
// Challenge: http://www.freecodecamp.com/challenges/bonfire-mutations
// Learn to Code at Free Code Camp (www.freecodecamp.com)

function mutation(arr) {
var elem0 = arr[0].toLowerCase();
  var elem1 = arr[1].toLowerCase();

  for(var i = 0; i < elem1.length; i++){
    var check = elem0.indexOf(elem1[i]);
    if (check === -1){
      return false;
    }
  }
  return true;
}
mutation(["hello", "hey"]);